A high reliability semiconductor package typically includes a semiconductor device which is hermetically sealed in a housing portion thereof. Typical semiconductor devices used in high reliability semiconductor packages are power MOSFETs, bipolar transistors, Schottky diodes, PN junction diodes, and IGBTs.
Hermetic surface mount packages, leadless chip carriers and ceramic leadless chip carriers (also known as LCC and CLCC respectively) have served as high reliability platforms for more than 20 years.
In the recent years, a vast array of electronic designs have been integrating new surface mount packages (also referred to as surface mounted devices or SMDs) which have surface mountable terminals on a common surface thereof. Such SMDs are desirable due to their smaller size and footprint, lighter weight, and excellent thermal performance. In addition, many high frequency circuit designs benefit from the inherently low inductance and low resistance of such SMDs.
U.S. patent application Ser. No. 11/044,933, assigned to the assignee of the present application and incorporated by reference, discloses a hermetically sealed package which includes a substrate having an opening therein, a power semiconductor switch disposed within the opening, four terminals brazed onto one major surface of the substrate near the mouth of the opening on the first surface of the substrate, another terminal attached to a second opposing major surface of the substrate and hermetically closing the mouth of the opening at the second surface of the substrate, and a cover hermetically closing the mouth of the opening at the first surface of the substrate. The terminal on the second surface of the substrate serves as an electrical terminal and a thermal path for the heat that is generated by the power semiconductor device.
The terminals are formed from an alloy of tungsten and copper. The low electrical resistivity and thermal properties of tungsten copper impart desirable characteristics to the package. Specifically, the low electrical resistivity of a tungsten copper alloy allows for higher current handling and thus lower power dissipation, and its coefficient of thermal expansion improves the reliability of the package, making it suitable for high reliability applications.
U.S. patent application No. Ser. No. 11/042,986, assigned to the assignee of the present application and incorporated by reference, discloses another hermetically sealed semiconductor package suitable for use in a power module according to the present application.